The Auth0 Next.js SDK is a library for implementing user authentication in Next.js applications. Versions 4.9.0 through 4.12.1 contain an input-validation flaw in the returnTo parameter, which could allow attackers to inject unintended OAuth query parameters into the Auth0 authorization request. Successful exploitation may result in tokens being issued with unintended parameters. This issue is fixed in version 4.13.0.
The product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are not allowed by policy or otherwise require other action to neutralize before additional processing takes place, but the list is incomplete.